Elemental Rebuke

When you are hit by an attack roll, you can take a Reaction to halve the attack's damage against yourself (round down) and force the attacker to make a Dexterity saving throw against your spell save DC. On a failed save, the attacker takes damage equal to 2d10 plus your Charisma modifier of one of the following types (your choice): Acid, Cold, Fire, Lightning, or Thunder. On a successful save, the attacker takes half as much damage.

You can use this feature a number of times equal to your Charisma modifier (minimum of once), and you regain all expended uses when you finish a Long Rest.